Control of electric motors



B. W. JONES.

CONTROL OF ELECTRIC MOTORS. APPLICATION HLED MAY 20'. 1918.

Patented July 27 His o fttorneg.

Inventor". Beqj am in W Jones,

UNITED STATE-S17 PATENT OFFICE.

BENJAMIN W. JO1\TES, or sciiinnac'r imz, NEW YORK assieivoa To GENERAL ELECTRIC COMPANY, Aconrena'rionon new YORK. v I w h conrnot or ELECTRIC MOTORS.

To all whom it may concern: Be it known that 1,-BENJAM1NWV; JoNns,a

citizenv ofthe United .States, residing. at

Schenectady, in the county of Schenectady, State of'New York, have invented certain new and useful Improvements in Control of Electric Mt0rs,of which'the following is a I specification. V

1 cfiicient manner.

This invention relates to the control ofelectric motors and has for its object the provision of improved'means whereby a starting resistance maybe automatically cut out of the motor circuit in a ,simple,reliable and My invention relatesmore specifically to the starting oiian alternating current motor of the wound rotontypein which a resistance is employed to bring the motor up to speed gradually and-safely.- My invention finds 'a ready application in thestarting of three phase motors, particularly where at starting the resistance sections are connected in delta. One of theobjectsof my invention is to provide meanslwhete'by, a resistance so connected may be reduced in such a manner that all of the resistance is in circuit during the starting period andthe total resistanceis reduced graduallyrand at a proper rate. r In carrying outfmy invention LlILOIlG' form, I first connect; the resistance'sections in delta to give the maximum resistance, Whenfthe motor current? drops to a prede terinined value the intermediate points of the three legs areconnected together, t hereby making what night ,be called a multiple Y connection, each leg being formed; by two halves of the deg connected, in inultiple. T'lllS reduces the resistance by a definite perz centage. Thenext step, Wh'ch 'n the par- 3 ticular arrangement shown will be taken when the current drops to the predetermined value, consists in breakingthe connectionof the intermediate points 'to each other and connecting these intermediate points togthe ends of the sections, the intermediate point of eachsection being connected toethe'poi nt" of connection of tlie other-two legs This, makes what might be called agmultiple delta connection, since the connection will now be a delta in which each leg is composed of two halves of a legconnected in multiple, and" thecresistance willlhe again reduced. The final stepwhich will be taken at the proper time consists in restoring the first intermediate step a while maintaining the second inter-:

, specificafibnor meane t Patented-July 2*7, 1920. v Application fi 1ed May 2Q, 1918. Serial No. 235,437f v mediate step,'the result beingto short cir-- cuit each leg' and entirelysho'rt circuit the r rotor. Further ohjectsand purposes ofjmy invention will. appear .in the course of the following specification, in which I have shown my invention embodied-in concrete 7 formi'torpurposes 101: illustration; I

. c In the accompanying" drawing illustrat- 7 ing one form of my invention Figure 1-is a diagrammatic view of a system of control foran alternatingcurrent motor, and Figsi- 2, 3, land-'5 show how the resistance sections' are connected in the various steps. Referring to the drawings, M represents a motor to be controlled and in the arrangement shown is athree'phase slip ring motor to which are'permanently connected the rev sistance sections R,.R'. and R The perma-- nent connectionsto the sliprings are made inideltaalthough'tliis connection is not es- S611l3ltl130 my invention." Electro-magnetic allyoperated switch 11, is arranged to cone nect the. motor to the line; .Contactor 12,- which is the first :to close after the closure of switch 10, makes the :connectionof the resistance sections shown in- Fig. 3 and con tactor 13, which closes after switch 12, makes the connections oit'the resistance section shown in Fig. 4. The final step which is accomplished by the closure of switchil2,

v switch or cont actor 10,00ntrolledby a manuv while switch 13, is closed, establishes'the connection of the resistance shown inFig 5. The closure'offswitchesj12 andj13 is underthe control of the motor current, and to this end Iprovide the two current limitrelays 1a and 15 The closure ofcontactor 12 is I under the control of the-current limit relay 14: and the closure of contactor is under the control of current limit relay 15. Current limit 'elay -l l, therefore operates twice mined value thecontactor 12:will again close while the contactor-13 remains closed.

Referring now to the specificconnections,

it will be noted'that the contactor 10 is provided with an interlock 16,'one contact of I which :is connected to the windingof contactor 12 while theother is connected to a .contactof the series relay 15 Closure of V eration of my the contaetor 10, therefore, energizes the contactor 12 when the current determined value and the series relay 11 drops. The contactor 12 is provided with three interlocks one of which, 17, opens the actuating circuit of the contaetor 13, while interlock 18 makes a maintaining circuit for thecontactor 12, independently of the cur-' rentlimit relay 14. The interlock 19 makes a circuit for the shunt core of relay 15. Contactor 13 is provided with two interlocks, 21

and 22 for purposes hereinafter described.

The two current limitrelays 14: and 15, are of substantially the same type, the former consisting of a series winding controlling a contact 23 in the controlled circuit, the contact being normally raised so as tobe ready for connection and released by a shunt coil 24 operating upon a pivoted lever 25, the end of which supports the contact 23. This is a well. known form of current limit relay and requires no description. The current relay 15 differs from current relay 14 in merely that there are two. contacts 26 and 27, one of which is, closed when the relay is in its raised position and is open in its lower position by reason, of the drop of the current. There is also provided a contact 20 for purposes hereinafter described.

As thus constructed and arranged the opimproved system is as follows: In the. drawings the parts are all shown in the positions which they assume when the control switch 11 is open. To start the motor the control switch 11 is closed, thereby completing the circuit from line a through the winding of contaetor 10 to line b, contactorlO thereupon'closes and completesthe motor circuit. The connections of the resistance sections It, R and R are now the permanent connections, which is a delta connection, shown in Fig. 2. The closureof contaetor 10 connects the wil'iding 1 to one side of the line andenergizes the shunt winding 2ft of the current limit relay 14, thereby releasing the contact 23150 the control of the series winding. VVhenthe current drops to the proper value, due to the speeding up of the motor, the contact 23 will drop and the circuit for the contactor 12 will be completed from the line a, conductor 28, through the upper contact of the series relay 15, through the interlocking contact 16, winding of; contaetor 12, and through the contact 23 to line b. The closing of the relay contact 23 short circuits the shunt winding 24 of the relay so that the contact 23 will be again raised, but in the meantime the contaetor 12 having closed, makes a maintaining circuit for the contactor through the interlock 18 and con-' ductor 29 independently of the relay contaetor 23. The closing of the contaetor 12 makes the connections shown in Fig. 3, in which'it will be observed that the intermedrops to a pre-.

obvious from Fig. 1.

diate points of the resistance are connected together. I have shown the intermediate point of the resistance as being the middle point although in practice this is not essen tial; in fact, in many cases it may be advisable to have one part greater than the other. The connections to the contaetor 12 whereby the intermediate points are connected together will be clear from Fig. 1.

In order to illustrate how the value of the total resistance in circuit is reduced in the various steps, I shall assume the value of two for each of the resistance sections R, R? and R Since as shown, the intermediate connectionis at themiddle point, each half section will have a value of one. The first step, with the contaetor 10 only closed, and the resistance in full delta, the resultant three-phase resistance will be one-half of 1.33 as is well understood. When the second step is taken and the connection shown in Fig. 3 established, the resultant three phase resistance will be reduced to onehalf of one, so that the closing of the cont-actor 12 has reduced the resistance in the ratio of 1.33 to 1, all the resistance being in circuit.

Proceeding now to the next step, the closing of the contaetor 12 energizes the shunt coil of the current limit relay 15, thereby releasing the relay to the control of the motor current, the circuit being from line a, through conductor 7 28, through the shunt coil, through the interlocking contact 19 of contaetor 12 and interlocking contact 21 of contaetor 13 to line b. The relay 15 is now, therefore, under'the control of the motor current so that when the current drops to the proper value the plunger will drop and make the lower contact, thereby energizing the winding of the contaetor 13, the circuit now being through conductor 28, contact 27 of the current limit relay, interlock 17 of contaetor 12, which has now opened due to its winding being deenergized at contact 26, winding of contactor 13 and'back to line b. The closing of contaetor 13 makes the connections shown in Fig. 4, from which it will be seen that theintermediate point of each section is connected to the junction point of the other two resistances. This makes what may be called a double delta connection since each leg is now composed of the two halves of theleg connected in parallel. This connection will reduce the resultant threephase resistance to one-half of .33, as is well understood. The connections to the contactor 13 whereby this is accomplished will be The closing of contactor 13 opens the circuit of the shunt coil of current limit relay 15 at the interlocking contact 21. The current limit relay will, therefore, make its upper. contact in which the shunt winding of the relay 14 will be energized as before described, so that when the current drops to a predetermined value,

the contact 23 of the relay 2e will drop and establish a circuit 'for' the Winding of the from which it will beseen that all of the re- 7 sistance sections are short circuited. It will thus be seen thatthe' total resistance in. cir-' cuit is gradually reducedunder the control of the motor current from a maximum in which the sections of resistance are con- 7 nected in full delta to a minimum vhich in namely contaotor connection thereto of this case is a complete short circuit of. the resistance, while maintaining all of the resistance in circuit during the cycle. over, the current phases. use is made of the resistance and the steps are properly graduated. It will also be noted thata minimum number of contac tors are used, since one of the' contactors,

12, 1S used twice.

\Vhile I have described my invention as embodied in concrete form-and as operating in a specific manner 1n accordance with the provisions of; the patent statutes, it should be understood that I do not limit my invention thereto as various modifications will suggest themselves to those skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure 7 by Letters Patent of the United States, is

1. The combination with a three-phase motor and a resistance section for each phase connected together at theirends ofmeans automatically operated responsively to themotor current for connecting an intermediate point tions and then connecting the intermediate points to the ends of the sections while maintaining all the resistance in circuit to reduce the resistance in'themotor circuit.

2. The combination with a three-phase motor and resistance sections having a delta operated responsively to the'motor current r for connecting an intermediate point of each of said sections to an intermediate point of then connect-- each of the other sections and I ing each intermediatepoint to' the ends of the other sections while maintaining all the resistance in circuit to reduce the resistance in the motor circuit.

3. 'The combination with a three-phase motor and resistance sections-having a delta connection thereto'of means for connecting an intermediate point of each of said sections to'an intermediate point of each of the More" is kept balanced in all the The result" is that a most .efiicient.

of each of said resistance sections to intermediate points'of the other secf means automatically ing this first other sectionsto reduce the resistance in the motor ClICIlltL -,4.-T11e combination with a tl'iree-phase motor and resistance sections having a delta" connection thereto of means for first connecting an intermediate point of' each of a said sections to an intermediatepoint ofthe other sections to reduce the resistance, and

then connecting the three intermediate points I tor and a resistance section connected to' each phase and connected together at their ends, of means forconnecting an interme diate point of each of said resistance sections to the ends of the other two sections while maintaining all of the resistance in circuit to reduce the total resistance in the motor circuit. 7

6. The combination with a polyphase mo- 'tor and a resistorconnected'to each phase-the resistors being: connected together at their ends, ofmeans-for connecting two parts of each resistor in parallel with the ends of each section thus formed of two parallel parts joined to reduce the total resistance in the motor circuit.

"7. The combination with a three phase motor and three resistors having a delta connection thereto, of means for connecting two parts of each resistor in parallel and connecting the sections thus formed of the parallel parts together at a common point to form a Y connection.

8. The. combination with a three-phase motor and three resistors having a delta connection thereto,of means for connecting two parts of each resistor in parallel with the ends of the sections thus formed of the parallel parts joined to form a delta connection to reduce the resistance in the motor circuit.

9. The combination with a three-phase motor and three resistors having a delta connection thereto, of means for connecting two parts of each resistor in parallel and connecting the three sections thus formed of the parallel parts successively in Y and in delta to reduce the total resistance in the motor circuit. p 10. The combination with a three-phase motor and resistance sections having a delta connection thereto of means for first connecting intermediate points of said sections together to reduce the resistance, then breakconnection and connecting the intermediate points to-the ends to further reduce the resistance, and finally restoring the first connection while maintaining the second connection to short circuit the relate point of each section to the necting-an intermediate point of each of said sections to an intermediate point of each of the other sections to reduce the resistance, and subsequently connecting the intermediends of the othersection with the first connection maintained to shortcircuit the resistance.

12. The combination with a three-phase motor and a resistance section for each phase connected togetherat their ends, of two electro magnetic switches for controllingsaid resistance and connections whereby one of said switches closes to connect points of said resistance sections together followed by the closure of thesecond switch and the opening of the first switch to connect the intermediate points to the ends of,

the sections, ;and finally the two switches close to short, circuit the resistance.

13. The combination with a three-phase; motor and resistance sections hav ng a delta connection thereto, of two electromagnetic switches for controlling said resistance,,and connections-wherebyl closing one of said switches connects an intermediate point of each of said sections to an intermediate point of each of the other sections, closing the second switch and opening the first connects the ntermediate polnt of each section to intermediate the ends of the other sections, and finally closing the first switch with the second maintained closed short circuits the resistance sections. I V i 14. l he combination with a three-phase motor and resistance sections having a delta connection thereto, of two electromagnetic switches for controlling said resistance, means responsive tothe motor current for controlling the said switches, and connections whereby the first of said switches will automatically close and connect an intermediate point of each of said sections to an intermediate point of each of the other sections when the current drops to a predetermined value, next the second of said switches will automatically close and the first automatically open to connect the intermediate point of'each section to the ends of the other sections when the current drops toa predeterminedValue, and finally the first switch will automatically close and the second switch be maintained closed to short circuit the resistance sections when the current again drops to a predetermined value.

In witness whereof I my handthisl'ftlr day of May, 1918.

1 BENJAMIN w. JONES.

have hereunto set 

